The present invention relates to an improved grinding wheel and, more particularly, to an improved grinding wheel of the type suitable for heavy grinding and for processing of materials which are difficult to grind; and to a method of manufacturing such a grinding wheel.
A grinding wheel using a so-called sintered hard abrasive such as diamond, silicon nitride or boron nitride has an abrasive grain acting as a cutter which has high hardness, superior durability and abrasion resistance. Such a grinding wheel has been used for grinding and processing a variety of processed materials as well as for processing a variety of materials which are difficult to grind, such as sintered hard metals, stone materials, concrete, glass and ceramics. Grinding wheels of this type metal bond grinding wheels, resinoid bond grinding wheels, and vitrified bond grinding wheels are generally known as grinding wheels of this type. These are classified according to the material used as a binder for the abrasive grains. It is also known that performance of these grinding wheels varies greatly according to the kind and structure of the binder.
FIG. 1 illustrates the inner structure of a metal bond grinding wheel using a metal such as nickel as a binder, in which abrasive grains 1 are held by a binder 2. The binder 2 has a strong bonding ability for abrasive grains and is superior in durability and abrasion resistance, while it is poor in the sticking ability to processed materials and the cutting quality and insufficient in the formation of chip pockets resulting in easy stuffing. As a result, a grinding wheel having a relatively low abrasive grain density of about 75 is usually used, but this still has a poor grinding efficiency such that no sufficient effect on heavy grinding and the processing of materials hard for grinding has been presented. Compared with a metal bond grindstone, a resinoid bond grinding wheel using an organic polymer material as a binder is superior in the sticking ability to processed materials and the cutting quality, while being so poor in the ability of holding abrasive grains that the grains are prone to become removed. The grinding wheel of this kind is accordingly unsuitable for heavy grinding and the processing of materials difficult for grinding. This also applies to a vitrified bond grinding wheel. In order to solve the problems prevailing in conventional grindstones, an example as illustrated in FIG. 2 has been proposed, wherein an organic or inorganic binder 2 is formed in a porous form and metal particles 3 are impregnated in the pores so that the ability of holding abrasive grains is improved. Such a grinding wheel, however, has a basic structure such that the organic or inorganic binder 2 holds the abrasive grains 1 mainly so that its performance is not expected to be improved to a remarkable extent.